Feb 11, 2010
If you want the code server side then use asp.net AJAX toolkit, if you want the code client side then use jQuery, or just write your won js.
jQuery does give you much more control over your js but on the other had the AJAX toolkit makes it so you dont have to know js.
Feb 15, 2010
jQuery making dealing with HTML/DHTML (UI) easier without postback (and using browser capabilities) while it also supports connecting to web services for data retrieval. ASP.NET AJAX is to reduce visible server post-back and less of DOM-based UI manipulation. I strongly suggest to go with both because both combinely give lot of power.